Populate Error Message

Hello guys,

i have the attached Excel which works fine.
it's a Planning tool that i use in order to visualize appointment from a table.

what i would like to add to this is an error message that will display if i book 2 appointments at the same time on the same desk.

in the file for example i have booked company Delta and Charly same day, dame location, same desk with overlapping times

what do you think the best way to do that would be?

Thank you

in row 10 and down
=SUM(((J10=$J$9:J9)*(I10=$I$9:I9)*IFERROR((IF(E10+H10>$E$9:E9+$H$9:H9,$E$9:E9+$H$9:H9,E10+H10)-IF(E10+F10>$E$9:E9+$F$9:F9,E10+F10,$E$9:E9+$F$9:F9))^0.5,)>0)*ROW($A$1:A1))
as array formula
looks through rows above and returns row#, if there is overlap with it

Hey Tim,

Tried to apply the formula but i am not able to make it work, nothing shows up on the right hand side.

uploaded the file